The long term goal of this research project is to characterize unsaturated fatty acid biosynthesis of rat aorta and to study the effect of feeding diets of varying fatty acid and cholesterol content on this process. Unsaturated fatty acids have two distinct roles: to regulate membrane fluidity and to participate in cholesterol ester synthesis. Dietary fatty acids regulate unsaturated fatty acid biosynthesis in liver but the effect of these diets on unsaturated fatty acid biosynthesis in the aorta is not known at this time. Cholesterol feeding has been shown to stimulate cholesterol ester synthesis in the aorta and it is assumed that the necessary unsaturated fatty acid is biosynthesized by the aorta. Rats will be fed diets containing cholesterol and either polyunsaturated fatty acids or saturated fatty acids for six to twelve weeks and later for six month periods. Some control rats will be fed either saturated of polyunsaturated fatty acids and other control rats will be fed chow diets. Some enzymatic and physical properties of rat aorta will be studied. Enzymes to be assayed include: the enzymes of unsaturated fatty acid biosynthesis, cholesterol ester synthesis and hydrolysis, and the microsomal electron transport chain. The effect of some drugs used to lower cholesterol in humans will be tested as inhibitors of these enzymatic reactions. Some physical properties of the aorta to be monitored include lipid composition of the cell membranes and the fluidity of these membranes. Correlation of these physical and enzymatic changes in other tissues including the liver, plasma and adipose tissue should result in a clear understanding of how the total rat organism responds to cholesterol and fatty acid components of the diet. Inclusion of polyunsaturated fatty acids in diets of humans is recommended therapy for prevention of atherosclerosis but the biochemical basis for this recommendation is not established. It is anticipated that this study will provide basic biochemical information on the effects of diets of varying fatty acid and cholesterol content on physical and enzymatic properties of the aorta.